1. Field of the Invention
The present invention relates to coating compositions containing nanosized colorants, more particularly to coating compositions containing a plurality of nanosized colorants having low haze (high transparency) and a narrow absorbance bandwidth in the visible spectrum.
2. Prior Art
Paint compositions typically include colorant particles dispersed in a resinous binder. The paint composition may further include reflective pigments such as aluminum flake or mica or other color effect pigment compositions or substrate-hiding materials such as titanium dioxide or zinc oxide or lead oxide. The colorant particles used in conventional paints are typically on the order of 0.5 micron in size. Particles of this size absorb light at certain wavelengths and scatter light at other wavelengths. This partial absorption and partial scattering creates a degraded coloration effect when viewed by an observer. Selection of a particular color for a paint requires blending of such colorants and is difficult to achieve using conventional colorants because the colorants have spectral characteristics that overlap one another and because the degrading scattering effects are compounded. As a result, conventional paint compositions typically require blending mixtures selected from of tens or even hundreds of various colorants in order to achieve a desired paint color. To create a paint color on demand, paint suppliers maintain numerous colorants on hand to be able to blend any combination of colorants.
When a new color of a paint composition is desired, several colorants are mixed together and balanced in order to achieve the desired color. This process of producing a colored paint is significantly complicated when the end product is intended to match an existing paint composition. For example, in automotive refinish paints, it is desirable to produce a paint composition that closely matches the paint on an automobile. The color of a paint formulation originally painted on the vehicle during production may change over time and with weathering. In addition, the spectral characteristics of the colorants of the original paint formulation may not be the same as the spectral characteristics of later available colorants. Due to these variabilities, the process of preparing a paint composition that closely matches that of an existing automobile is complicated and often requires trial and error until the desired color is achieved.
Accordingly, a need remains for a method of preparing a protective and decorative coating for applying to a substrate and having a color which is either prespecified or matches a preselected coating composition selected from a minimum quantity of colorants.